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Replaced Motherboard In SONY LED TV Model KDL-40NX650

By on December 3, 2022
Replaced Motherboard In SONY LED TV Model KDL-40NX650







led tv repair

This TV belonged to a doctor, who had kept it aside for a very long time, as he bought a new one. The reasons was that when the TV was taken to the company, they held it with them for weeks saying that the boards were defective and replacement was awaited. So, he took it back and bought another one. During one of my visits to his home, he requested me to look into it. But weeks, months and perhaps years passed, before the TV was sent to me. Though he would enquire whether he could send the TV whenever we meet on any social gathering, it never took place, until I prompted him to bring it as I had developed a tie-up with my Techie Friend, who opened a Panel Bonding shop around 20 KMs away and I was frequenting my visit there. As the TV was very heavy, I requested the Auto driver who brought the TV to my home, to load it into my car, the rear seat of which was pushed down to use it as a van. This facility to push down the rear seat allowed me to carry a few TVs at a time. I had around three TVs with me.

On reaching my friend’s place, he asked his partner to bring the TV to the first floor, where he had set up his shop in a shopping complex. On switching on, there was no power indication and it was totally dead. The TV was opened for further checkup and investigation. The power supply was working and luckily the company had not put any other defective boards in place of working boards, which they are practiced to do on customer sets that are totally dead, and are called back. The companies resort to this malpractice apart from charging minimum for opening and closing the set calling it as estimate charges. In fact, we, technicians, cannot even imagine charging a customer, when the efforts become futile in spite of spending several hours on a set. Here you can have a look at inside of this TV:

how to fix led tv

After conducting checks on the mother board, where the secondary supplies were intact, my friend was of opinion that the uController would have failed and it is not an easy task to revive this board with so many tiny components fit on both sides of the board. We had two options in front of us: Go for working boards from vendors who deal in such removed boards from panel defective TVs which they bought for such salvaging works, or fit a Universal Board U11. Before that we had to ensure that the panel was working, for which the backlight should be switched on. So, I connected 10K resistors from the 12V supplies to Power On and Dim pins. My friend checked the backlight using a Tester after disconnecting it from the inverter section and found it was working. Then we connected the backlight to its own inverter and switched on and it worked. Surprisingly, it was showing around 215V when we checked the voltage. So, he took the TV to his panel servicing section and applied a signal from the panel tester he had and got the following result:

testing led tv

As you can see, it had an aura like white thick line on all the four sides. My friend told that this TV, which had its thick front glass affixed on the panel with glue, used to develop moisture in the gap between the glass and panel, when left unused for a prolonged time and this moisture will reflect like this. The option was removing the glass forcefully using either hot blower or cutting in from the sides, both of which are risky as the panel or glass itself might break in the process. My techie friends were of opinion to leave it as it was and inform the customer and go ahead further only if he agrees to accept the TV in this condition.

The moisture might disappear after the TV is back to use like what we see in a wrist watch. I spoke to the customer and told him three things (1) About this special ‘aura’ on the screen (2) Option of going for a used board which was not only expensive but there was no guarantee (3) Use a U11 Universal Board, which was cheaper and had six months’ guarantee. I also told him about the estimated expenses. He agreed for option (3) accepting the inherent defect on the screen and also paid the full estimated money as advance on my request. My friend ordered for a U11 board and we two worked on fitting this board on the TV in place of its mother board. My friend wired the speakers, 12V power supply, IR and power indicator on the front side and finally the LVDS cable to the T-con board after doing slight modifications for correct fit. The TV worked very well when checked before putting the back cover.

back cover of led tv

Though I am writing this as if all these things happened as a continuous process on the same day, in reality the TV reached this stage only after several visits to his shop and after I almost sat on his head. Because there were such pressure of work that this got sidelined, until I put my foot down. The cost? I had to stay until 12 midnight to get it ready and load it back to my car. It was raining very heavily when I drove and reached home by around 1 AM! My wife

was very much distressed for taking such risks at my old age (73 running now!) But I pacified her that it rarely happened and justified the reasons.

I informed the doctor next day that I had brought the TV home and the TV would be ready for pick up after finishing some cosmetic work to cover holes on the back cover (holes unfilled due to change of mother board) and testing it for a couple or more days. Then, when I wanted to check the TV, I noticed that I had forgotten to pick up its remote, without which it will not work, as the Universal Board had no key board for fixing. So, did one more visit to the shop next day morning. This time I went there by bus to economize the abnormal cost adding up on an already committed case. My friend detained me for servicing three more sets before I could return in the evening. There was rain as usual, but I had remembered to carry an umbrella. Surprisingly, the bus that I boarded was the same that I had used in the morning, adding up my amusements!

When I switched on the TV next day, there was no display, though the panel backlight was on! So, I had to remove all the screws and open the back cover to see what happened. On checking, I found that the LVDS cable had come off from the main board! Something that would have happened while driving in the night, over some pot holes on the road, which could not be seen because of water logging. Well, after fixing it back and fastening it well with a cloth tape, I put only four screws and again tried the TV. It worked very well for about 15 minutes and then became dead! Totally dead! So, I deduced that when the back cover was fixed, it increased the temperature inside and the power supply shut off itself when it exceeded the limit fixed; a normal protection action that was designed in many branded TVs. The next move was then to provide an SMPS cooling fan on top of the Power Supply Board and check. So, I removed the back cover once again, disconnected the Power supply board and brought it to my service table. (I had moved the TV for running check up to one of my other vacant bedrooms.) There was a place where 12V and ground could be tapped. I inserted a two pin male socket into the holes and soldered it. Then connected an SMPS fan and turned the Power Supply on and found that the Fan was rotating very well. See the pictures below:

how to fix a broken led tv

I re-tested the TV after fixing the back cover for almost 12 hours or more in a day for three days and it did not have any problem. So informed customer to come and pick it up. Mission accomplished with a big relief. Satisfaction in high intensity got collected to its bag as usual!

how to repair a broken led tv

This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.

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You may check on his previous article on Power Supply Failure Found In New Induction Cooker Board




  1. Andrew F. Ali

    December 3, 2022 at 10:19 am

    That's a lot of work!! I would have given up a long time ago. The feel of satisfction for completing an enormous task like this is undescribable and the sometimes lingering doubts at the back of one's mind is truly blessed. GREAT JOB and an EXCELLENT feather in your cap!!!!

    • Parasuraman S

      December 3, 2022 at 4:39 pm

      Many, many thanks for your encouraging words of appreciation!

  2. Waleed Rishmawi

    December 3, 2022 at 3:29 pm

    you actually created a new TV out of dead one although it was lots of work but I guess it was worth it. thanks for sharing and have a blessed day

    • Parasuraman S

      December 3, 2022 at 4:39 pm

      Yes, dear! It was worth it.

  3. Albert van Bemmelen

    December 3, 2022 at 3:39 pm

    That is a hell of a story for a very heavy Sony tv that afterwards is not exactly worth looking at, to put it mildly. And I guess it uses to much power anyway (a new important issue these days) and apparently afterwards also easily overheats. In this case I give your wife plenty reasons to be worried of your good health! Please take more care of your spare time Parasuraman and do not simply take on all hopeless repair cases! There is just so much we can do in one day at our age!

    • Parasuraman S

      December 3, 2022 at 4:41 pm

      Many thanks for your comments, concern and very valuable advice!

  4. Imoudu.O

    December 3, 2022 at 4:10 pm

    I don't even know what to say for this kind of extra mile you had gone to get this tv repaired, considering your age, for me I would have given up.All the same I still gain 1 or 2 things..Thanks for sharing, have a nice day sir.

    • Parasuraman S

      December 3, 2022 at 4:42 pm

      It is the force of the craze that drives us and keeps us going! Many thanks for your comments, dear!

  5. Mathew Charles Karonga

    December 3, 2022 at 7:19 pm

    Thank you for sharing.

    Your patience is unbelievable.

    Your perseverance is amazing and always challenge me.

    You are always there to add something new in your articles that make them worth reading and beneficial.

    Well done

    • Parasuraman S

      December 4, 2022 at 11:09 am

      Many thanks for your encouraging comments!

  6. Imoudu.O

    December 3, 2022 at 8:46 pm

    Sir, if I want to test backlight with use of 10k resistors on psb, do I have to isolate psb from main board before I power on?

    • Parasuraman S

      December 4, 2022 at 11:09 am

      Yes, you should!

  7. Tito Kanshulu

    December 4, 2022 at 9:41 pm

    Mr Parasuraman, this is an excellent work which, to me, has been accompanied by what we call, 'a dogged determination to catch the game.' This is the spirit of a real techie. Hat off

    • Parasuraman S

      December 5, 2022 at 3:40 pm

      Many thanks for your very encouraging comments!

  8. Yogesh Panchal

    December 5, 2022 at 1:14 am

    Sir,I felt like i was with you on the service......good write up.

    • Parasuraman S

      December 5, 2022 at 3:41 pm

      Many thanks Yogesh! I love writing Techie Novels! (LOL)


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